'\" t
.TH "SD_JOURNAL_STREAM_FD" "3" "" "systemd 256.7" "sd_journal_stream_fd"
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
sd_journal_stream_fd, sd_journal_stream_fd_with_namespace \- Create log stream file descriptor to the journal
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-journal\&.h>
.fi
.ft
.HP \w'int\ sd_journal_stream_fd('u
.BI "int sd_journal_stream_fd(const\ char\ *" "identifier" ", int\ " "priority" ", int\ " "level_prefix" ");"
.HP \w'int\ sd_journal_stream_fd_with_namespace('u
.BI "int sd_journal_stream_fd_with_namespace(const\ char\ *" "name_space" ", const\ char\ *" "identifier" ", int\ " "priority" ", int\ " "level_prefix" ");"
.SH "DESCRIPTION"
.PP
\fBsd_journal_stream_fd()\fR
may be used to create a log stream file descriptor\&. Log messages written to this file descriptor as simple newline\-separated text strings are written to the journal\&. This file descriptor can be used internally by applications or be made standard output or standard error of other processes executed\&.
.PP
\fBsd_journal_stream_fd()\fR
takes a short program identifier string as first argument, which will be written to the journal as SYSLOG_IDENTIFIER= field for each log entry (see
\fBsystemd.journal-fields\fR(7)
for more information)\&. The second argument shall be the default priority level for all messages\&. The priority level is one of
\fBLOG_EMERG\fR,
\fBLOG_ALERT\fR,
\fBLOG_CRIT\fR,
\fBLOG_ERR\fR,
\fBLOG_WARNING\fR,
\fBLOG_NOTICE\fR,
\fBLOG_INFO\fR,
\fBLOG_DEBUG\fR, as defined in
syslog\&.h, see
\fBsyslog\fR(3)
for details\&. The third argument is a boolean: if true kernel\-style log level prefixes (such as
\fBSD_WARNING\fR) are interpreted, see
\fBsd-daemon\fR(3)
for more information\&.
.PP
\fBsd_journal_stream_fd_with_namespace()\fR
is similar to
\fBsd_journal_stream_fd()\fR, but takes an additional
\fIname_space\fR
parameter that specifies which journal namespace to operate on\&. If specified as
\fBNULL\fR
the call is identical to
\fBsd_journal_stream_fd()\fR\&. For details about journal namespaces, see
\fBsystemd-journald.service\fR(8)\&.
.PP
It is recommended that applications log UTF\-8 messages only with this API, but this is not enforced\&.
.PP
Each invocation of these functions allocates a new log stream file descriptor, that is not shared with prior or later invocations\&. The file descriptor is write\-only (its reading direction is shut down), and
\fBO_NONBLOCK\fR
is turned off initially\&.
.SH "RETURN VALUE"
.PP
The call returns a valid write\-only file descriptor on success or a negative errno\-style error code\&.
.SH "SIGNAL SAFETY"
.PP
\fBsd_journal_stream_fd()\fR
and
\fBsd_journal_stream_fd_with_namespace()\fR
are "async signal safe" in the meaning of
\fBsignal-safety\fR(7)\&.
.SH "NOTES"
.PP
All functions listed here are thread\-safe and may be called in parallel from multiple threads\&.
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.SH "EXAMPLES"
.PP
Creating a log stream suitable for
\fBfprintf\fR(3):
.sp
.if n \{\
.RS 4
.\}
.nf
/* SPDX\-License\-Identifier: MIT\-0 */

#define _GNU_SOURCE 1
#include <errno\&.h>
#include <syslog\&.h>
#include <stdio\&.h>
#include <unistd\&.h>
#include <systemd/sd\-journal\&.h>
#include <systemd/sd\-daemon\&.h>

int main(int argc, char *argv[]) {
  int fd;
  FILE *log;

  fd = sd_journal_stream_fd("test", LOG_INFO, 1);
  if (fd < 0) {
    fprintf(stderr, "Failed to create stream fd: %s\en", strerror(\-fd));
    return 1;
  }

  log = fdopen(fd, "w");
  if (!log) {
    fprintf(stderr, "Failed to create file object: %s\en", strerror(errno));
    close(fd);
    return 1;
  }
  fprintf(log, "Hello World!\en");
  fprintf(log, SD_WARNING "This is a warning!\en");
  fclose(log);
  return 0;
}
.fi
.if n \{\
.RE
.\}
.SH "HISTORY"
.PP
\fBsd_journal_stream_fd()\fR
was added in version 187\&.
.PP
\fBsd_journal_stream_fd_with_namespace()\fR
was added in version 256\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-journal\fR(3), \fBsd-daemon\fR(3), \fBsd_journal_print\fR(3), \fBsyslog\fR(3), \fBfprintf\fR(3), \fBsystemd.journal-fields\fR(7)
